Yes it is.
Easiest way is to set up a vlan with a new subnet for the wifi clients.Then set an outbound policy for traffic from that new subnet to use WAN2 and another for the normal LAN subnet to use WAN1. I would use priority outbound rules so that if one WAN fails the clients failover to the other WAN.
As Martin said or just let the your Balance balance the sessions between the two WANs and all devices.
By allowing the sessions to be balanced between the WANs give a much faster feeling internet for everyone.